1. Field of the Invention
The present invention relates to a multilayer filter that includes a plurality of LC parallel resonators including inductors having a loop shape and capacitor electrodes.
2. Description of the Related Art
A typical radio-frequency band-pass filter suited for miniaturization and low cost of manufacturing is configured such that a plurality of LC resonators is disposed in a laminate of dielectric layers and electrode layers.
Examples of such a multilayer band-pass filter are disclosed in Japanese Unexamined Patent Application Publication No. 2006-67221 and International Publication No. WO 2007-119356.
Japanese Unexamined Patent Application Publication No. 2006-67221 discloses a three-stage multilayer filter in which the first-stage and third-stage resonators are jump-coupled by a coupling capacitor C3, as illustrated in FIG. 1 thereof. The jump-coupling capacitor C3 is configured such that an electrode pattern 151 forming an inductor L1 and an electrode pattern 153 forming an inductor L3 face an electrode pattern 161, as illustrated in FIG. 3 thereof.
However, with the configuration described above, because the electrode pattern 161 also faces an electrode pattern 152 forming an inductor L2, unnecessary parasitic capacitance occurs between the electrode pattern 161 and the electrode pattern 152. Therefore, there is a problem in that Q of the filter decreases and attenuation characteristics deteriorate.
International Publication No. WO 2007-119356 discloses a configuration in which parasitic capacitance between an electrode pattern of a jump-coupling capacitor and a capacitance electrode pattern of a resonator that is not coupled to the electrode pattern of the jump-coupling capacitor is reduced.
FIG. 1 illustrates a configuration of a multilayer band-pass filter disclosed in WO 2007-119356. The multilayer band-pass filter illustrated in FIG. 1 includes a laminate including a ground electrode forming layer 601, a capacitor electrode forming layer 302, an input and output electrode forming layer 303, a line electrode forming layer 304, and an outer layer 305. Input and output electrodes 621 and 622 and an input-output intermediate capacitor electrode (electrode pattern of a jump-coupling capacitor) 160 are disposed on the input and output electrode forming layer 303. The input-output intermediate capacitor electrode 160 capacitively couples the input and output electrodes 621 and 622 by causing capacitance to occur between the input and output electrodes 621 and 622. Capacitor electrodes 311, 312, and 313 on the capacitor electrode forming layer 302 face a ground electrode 309.
To reduce parasitic capacitance between the input-output intermediate capacitor electrode (electrode pattern of a jump-coupling capacitor) 160 and the capacitor electrode 312 of the second-stage resonator, the capacitor electrode of the second-stage resonator is displaced from the capacitor electrodes of the first-stage and third-stage resonators in the plane direction of the laminate.
With the structure illustrated in FIG. 1, because the capacitor electrode of the second-stage resonator does not overlap the jump-coupling capacitor electrode when viewed from the direction in which the dielectric layers are laminated, the parasitic capacitance therebetween can be reduced.
However, the displacement of a capacitor electrode of a resonator in the layer direction (plane direction) increases the size of an area required for formation of capacitor electrodes, and there is a problem in that miniaturization of the device is difficult.